1. Field of the Invention
The present invention relates to a fixing apparatus, such as an electrophotographic copying machine and an electrophotographic printer, and an image forming apparatus including the fixing apparatus.
2. Description of the Related Art
As a fixing apparatus used in an electrophotographic copying machine or printer, an external-heating-type fixing apparatus that uses a film is known.
Such an external-heating-type fixing apparatus includes a driven heating roller, a pressure film unit that contacts the heating roller to form a nip portion, and a heating film unit that contacts a fixing roller to form a heating portion.
The heating film unit includes a tubular heating film, a heater that contacts the inner surface of the heating film, and a heating film guide that contacts the inner surface of the heating film and guides the rotation of the heating film. The pressure film unit includes a tubular pressure film and a pressure film guide that contacts the inner surface of the pressure film and guides the rotation of the pressure film.
This fixing apparatus enables the drive torque to be reduced more than a fixed-type external heating unit because the fixing apparatus uses a film that rotates with the heating roller even in an external heating unit.
In this fixing apparatus, the heating film and the pressure film are driven and rotated by driving and rotating the heating roller. Therefore, if the sliding resistance is large at the portion where the heating film guide that guides the rotation of the heating film and the inner surface of the heating film contact, rotation of the heating film can become uneven. Further, the same problem can also occur at the portion where the pressure film and the pressure film guide contact.
If the rotation of the heating film and the pressure film become uneven, the heat supply to the heating roller becomes uneven. Further, if the rotation of the pressure film becomes uneven, conveyance of a recording medium at the nip portion becomes uneven, which can cause uneven fixing.
Accordingly, in order to reduce frictional resistance between a fixing film and a film support member that contacts the inner surface of the fixing film, Japanese Patent Application Laid-Open No. 6-003982 discusses a fixing apparatus in which the film support member is provided with either ribs or holes that decrease the size of the sliding surface of the film support member with the fixing film. However, using the film support member (film guide) discussed in Japanese Patent Application Laid-Open No. 6-003982 in the fixing apparatus described above has the following problems. Specifically, during the fixing process, uneven gloss can occur in the region in which the portion where the heating film guide contacts the heating film and the portion where the pressure film guide contacts the pressure film overlap in the longitudinal direction of the heating roller.